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Countdown to the Venus transit on 6th June

Observers around the world are gearing up to observe (weather permitting) a rare planetary event on the morning of the 6th June 2012 (UK time). The transit of Venus, which sees the planet pass directly in front of the Sun, will not occur again for another 105 years, so this is likely to be our last chance to observe such an event. During the transit, Venus can be seen as a small black dot moving slowly across the face of the Sun over the course of a few hours. Although rare, Venus transits occur in pairs separated by just 8 years, however, the previous events were back in the years 1874 and 1882, whereas the next ones won't be until 2117 and 2125.

As the map below shows, the full transit will only be visible from countries around the Pacific region, however, observers in the UK will be able to catch the last hour (depending on location) once the Sun rises above the horizon on the morning of the 6th June. The nearly seven hour transit will start at 11:04pm on the 5th June and end at 5:54am the following morning, so you will need to be up before the crack of dawn (sunrise is around 4:52am in Liverpool) in order to prepare for the spectacle. Of course, times around the UK will vary, but some kind astronomers have created a useful tool that allows you to calculate exact times for your location.

World map detailing where the 2012 Venus transit can be seen fromCredit: NASA

The first ever transit of Venus was observed by the Liverpool astronomer Jeremiah Horrocks back in 1639. He used Kepler's laws of planetary motion to predict that Venus transits would occur in pairs, and calculated that the 1639 event would begin at around 3pm on the 4th December. Despite unsettled weather conditions, he was able to observe the transit less than an hour before sunset, and used his three measurements to estimate the size of Venus and Earth's distance from the Sun.

If you fancy trying to observe the last Venus transit for several generations, then the following tools may be of use: